On Sun, Mar 29, 2020 at 03:46:17PM +0200, Lars-Peter Clausen wrote: > On 3/29/20 1:34 PM, Rohit Sarkar wrote: > > On Sun, Mar 29, 2020 at 10:38:18AM +0100, Jonathan Cameron wrote: > > > On Sat, 28 Mar 2020 12:04:53 +0530 > > > Rohit Sarkar <rohitsarkar5398@xxxxxxxxx> wrote: > > > > > > > The debugfs_create_file_unsafe method does not protect the fops given to > > > > it from file removal. It must be used with DEFINE_DEBUGFS_ATTRIBUTE > > > > which makes the fops aware of the file lifetime. > > > > > > > > Further using DEFINE_DEBUGFS_ATTRIBUTE along with > > > > debugfs_create_file_unsafe significantly reduces the overhead introduced by > > > > debugfs_create_file which creates a lifetime managing proxy around each > > > > fops handed in. Refer [1] for more on this. > > > > > > > > Fixes the following warnings reported by coccinelle: > > > > drivers/iio/imu//adis16460.c:126:0-23: WARNING: adis16460_flash_count_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE > > > > drivers/iio/imu//adis16460.c:108:0-23: WARNING: adis16460_product_id_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE > > > > drivers/iio/imu//adis16460.c:90:0-23: WARNING: adis16460_serial_number_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE > > > > drivers/iio/imu//adis16400.c:278:0-23: WARNING: adis16400_flash_count_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE > > > > drivers/iio/imu//adis16400.c:261:0-23: WARNING: adis16400_product_id_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE > > > > > > > > [1]: https://lists.gt.net/linux/kernel/2369498 > > > > > > > > Rohit Sarkar (2): > > > > iio: imu: adis16400: use DEFINE_DEBUGFS_ATTRIBUTE instead of > > > > DEFINE_SIMPLE_ATTRIBUTE > > > > iio: imu: adis16460: use DEFINE_DEBUGFS_ATTRIBUTE instead of > > > > DEFINE_SIMPLE_ATTRIBUTE > > > > > > > > drivers/iio/imu/adis16400.c | 4 ++-- > > > > drivers/iio/imu/adis16460.c | 6 +++--- > > > > 2 files changed, 5 insertions(+), 5 deletions(-) > > > > > > > Hi Rohit, > > Hey, > > > You've opened a can of worms with this one. There as a previous series > > > posted doing exactly this change back in 2019 by Zhong Jiang (cc'd) > > > > > > At the time I did a bit of looking into why this had been universally taken > > > up cross tree and turned out there are some potential issues. > > > > > > Alexandru added it to the list of things to test, but I guess it got > > > buried under other work and is still outstanding. > > > > > > https://lkml.org/lkml/2019/10/30/144 > > Acc. to the patch by Zhong this change kind of comes off as a cosmetic > > change as in the commit message he mentions "it is more clear". > > > > But there is certainly more to it than that: > > In the current scenario since we are using debugfs_create_file_unsafe > > the file has no protection whatsoever against removal. > > The drivers you are patching all use debugfs_create_file() as far as I can > see. Ah, You are right. I dont know why I assumed that debugfs_create_file_unsafe was being used. Was probably sleepy when I sent this out :/ > The way I understand it using DEFINE_DEBUGFS_ATTRIBUTE without switching to > debugfs_create_file_unsafe() will not make a difference. There will only be > more overhead since the files are protected twice. That's right. it should either be ...unsafe() with DEFINE_DEBUGFS_ATTRIBUTE or what it is currently. In the current scenario the file is protected against removal but there is extra overhead because debugfs_create_file creates a lifetime managing proxy AFAIK. I can send a v2 changing the debugfs_create_file function to unsafe if someone can test it out on h/w as Jonathan suggested. > - Lars > Thanks, Rohit
